As used herein, an electric, electrical, or electronic machine (herein referred to simply as a “machine”) refers to any electromechanical device. Example machines include motors and generators. A single machine may be a motor, a generator, or operate as either a motor or a generator. When operating as a motor, a machine converts electrical energy into mechanical energy, and when operating as generator, a machine converts mechanical energy into electrical energy. Thus, it is understood that when a machine is said to “operate using” a certain type of power, it is meant that the machine is supplied with that type of power in motor mode and/or produces that type of power in generator mode.
As used herein, the term “synchronous machine” refers to a machine that operates using alternating current (AC) rather than direct current (DC). The speed of a synchronous motor, for example, is directly proportional to the frequency of the AC input. A synchronous motor that is supplied with a single AC input (or multiple AC inputs that have the same phase) is referred to as a “single phase” machine. In a single phase synchronous machine, all coils operate at the same phase. In a two-phase synchronous machine, some coils operate at one phase and other coils operate at another phase, usually 180 degrees from the first phase. Each phase may supply more than one coil.
One common type of synchronous machine is known as a “three-phase” machine because it operates using three-phase power, e.g., a three-phase motor is provided with three distinct AC inputs, each input being 120 degrees apart in phase from the other inputs.
FIGS. 1A and 1B are circuit diagrams illustrating possible coil configurations for a conventional three-phase machine. FIG. 1A illustrates the “Y” or “wye” configuration, and FIG. 1B illustrates the “delta” configuration. In each of FIGS. 1A and 1B, there are three power supplies, P1, P2, and P3, each of which produces an AC voltage that is 120 degrees apart in phase from the other two power supplies. The label “Px” where x=1 to N will hereinafter be used to refer to an AC voltage having one of N different phases, where each power supply is 360/N degrees apart from the power supplies that are next closest in phase. In each of FIGS. 1A and 1B, the three phase machine has three sets of coils, one set for each phase. The three sets are labeled A, B, and C, respectively.
The wye configuration can be considered a specific example of a general topology herein referred to as a “star”, in which all coils have one end tied to a common node, such as voltage ground. The delta configuration can be considered a specific example of a general topology herein referred to as a “polygon”, in which adjacent coils are connected in series in a single loop, with a power supply connected to each junction between two coils. The star and polygon topologies have different operating characteristics. For example, for a three phase 100V AC power supply, the maximum voltage across any coil in the star configuration is the maximum voltage measured between the power supply and ground, i.e., 100 Volts. The maximum voltage across any coil in the polygon configuration is the maximum voltage measured between one phase of the power supply and another phase of the power supply, i.e., ˜173 Volts.
Three phase machines have only two distinct coil configurations: wye and delta (“star” and “polygon”.) Changing the coil positions or the power connections does not create a new topology. In FIG. 1B, for example, the positions of coils B1 and C1 could be swapped, or power supply P1 could be swapped with power supply P3, but the topology (and performance) would not change. That is, however the coils and power supplies are rearranged, the maximum voltage across any coil in the three phase polygon configuration will not change. As will be seen below, the same is not true of multiphase machines.
As used herein, the term “multiphase” machine refers to machines that use or generate electricity of more than three phases. Example multiphase machines include five-phase machines, seven-phase machines, and so on. Multiphase machines may have even numbers of phases as well, although this is not common. Thus, as used herein, the term “multiphase” expressly excludes conventional three-phase machines.
FIGS. 2A, 2B, and 2C are circuit diagrams illustrating possible coil winding configurations for a conventional multiphase machine having five phases. FIG. 2A illustrates a five-phase star, FIG. 2B illustrates a five-phase polygon, and FIG. 2C illustrates what is herein referred to as an “N-angle” topology, e.g., the “pentangle” topology shown in FIG. 2C. Note that the difference between the pentagon configuration in FIG. 2B and the pentangle configuration in FIG. 2C is that in the polygon, one end of each coil is tied to one of the power supply phases and the other end of each coil is tied to another power supply that is closest in phase to the first power supply. For example, in FIG. 2B, one end of coil A is tied to P1 and the other end of coil A is tied to P2, which is 72 degrees apart in phase from P1.
In contrast, in the star configuration, one end of each coil is tied to one of the power supply phases and the other end of the each coil is tied to another power supply that is NOT closest in phase to the first power supply. For example, in FIG. 2C, one end of coil A is tied to P1 and the other end of coil A is tied to P3, which is 144 degrees apart in phase from P1. Five-phase machines have only three possible configurations: star, pentagon, and pentangle. For a 100V 5-phase power supply, the maximum voltage across each coil is 100 Volts for a star configuration, ˜118 Volts for a pentagon configuration, and ˜190 Volts for a pentangle configuration.
Multiphase machines have several advantages over conventional three-phase machines. For example, the failure of one phase of a three-phase machine, such as a wiring failure of that phase's coil or coils, may render the machine inoperable, e.g., because the remaining phases don't have the power to drive the load, or because the motor operation is unacceptably unbalanced. The failure of one phase of a seven-phase machine, on the other hand, may leave the machine with a sufficient number of coils and power. Likewise, the remaining six phases may be unbalanced, but within acceptable levels.
Additionally, in multiphase machines, the possibilities for the winding connections are greatly expanded from that of three-phase machines. For example, in a five-phase machine, there are three possibilities if the winding connection must form one group: the star, pentagon, and pentangle. Likewise, there are four possibilities for a single group winding connection in a seven-phase machine, i.e., star, heptagon, and two heptangles, each providing a different maximum voltage across each coil.
Since most public and private power grids provide three-phase power, multiphase machines must of necessity use three-phase power converted into multiphase power. This is typically done by rectifying the three-phase AC power to produce DC power, then using an inverter to convert the DC power to multiphase AC power. Devices that perform one or both of these steps to produce multiphase AC power are herein referred to as “converters.” A benefit of this necessity of using a converter to produce multiphase power is that multiphase machines are decoupled from the power grid.
Thus, multiphase machines have seen much development in the last ten years due to the development of converters which decouple machines from the grid, and the desire for higher performance machines within the same volume.
There are disadvantages associated with conventional multiphase machines, however. Perhaps because conventional multiphase machines tolerate the loss of a phase winding, conventional multiphase machines do not exhibit full winding redundancy. For example, multiphase arrangements with multi-star configurations have not been seen in the art. For this reason, conventional multiphase machines are not well suited for applications which are very sensitive to changes in total power or changes in balance or which require very high reliability.
Accordingly, in light of these disadvantages associated with conventional multiphase machines, there exists a need for redundant winding connections for multiphase electric machines.